Determining Fg

[Sprungmonkey]

Just wondering how people predict the final gravity so that determine when to do a diacetyl rest. Do you use the caculator in the yeast section of this forum.

 

[Sprungmonkey]

Also most resources I have read about diacetyl rests say to do it 2/3rds of the way though fermemtation. On white labs website they say:

To minimize the diacetyl attributes in beer, its recommended that the fermenting wort rest once the beer has reached terminal gravity for 48 hours at 62-70 degrees prior to crashing the temperature. This stage allows to yeast to reabsorb the diacetyl.

How does everyone else do it here?

 

[Adamt]

Doesn't really matter when you do a diacetyl rest... most do it with a little bit of primary to go, so that the elevated temperatures help finish off fermentation.

 

[lagers44]

To the first post about prediciting FG I use Beersmith which does the work for you , alternatively to do it manually you need the OG & the attenuation of the yeast & basic math.
i.e. OG 1.052 attenuation 67 - 75% ( average 71% ) therefore 52 x 71% = 36.9. 1.052 - 1.037 = 1.015 or at 75% FG is 1.013.
I'd like to hear if others do it this way as well or am I wrong doing this ?

Second post , you have 2 options. 1 after fermantation slowly raise the temp to about 18 -20C over a few days leave for 2-3 days then cooo again.
2. Leave in primary on yeast for another 1-2 weeks before racking , it usually achieves the same result unless you have extremely high levels & it's much easier.

Lagers

 

[Fourstar]

To the first post about prediciting FG I use Beersmith which does the work for you , alternatively to do it manually you need the OG & the attenuation of the yeast & basic math.
i.e. OG 1.052 attenuation 67 - 75% ( average 71% ) therefore 52 x 71% = 36.9. 1.052 - 1.037 = 1.015 or at 75% FG is 1.013.
I'd like to hear if others do it this way as well or am I wrong doing this ?

Second post , you have 2 options. 1 after fermantation slowly raise the temp to about 18 -20C over a few days leave for 2-3 days then cooo again.
2. Leave in primary on yeast for another 1-2 weeks before racking , it usually achieves the same result unless you have extremely high levels & it's much easier.

Lagers

If you're doing AG you should be able to callcualte attenuaton allot more accuratly as per your Mash tempratue. 60-64deg = Highest atttenaution

64>70 Deg lowest attenuation

As a lower mash temprature creates a much mroe fermentable wort it will also help you see if your thermometer is out as i did.

I went from doing brews that should have reached 5.5% alc.vol and were only fermenting out to 3.5-4%

Repalced the thermometer and my robust porter i estimated for 6.0% and is at 6.5% now and still fermenting!

(my efficiency increased by 4% aswell for some unknown reason.)

 

[lagers44]

If you're doing AG you should be able to callcualte attenuaton allot more accuratly as per your Mash tempratue. 60-64deg = Highest atttenaution

64>70 Deg lowest attenuation

As a lower mash temprature creates a much mroe fermentable wort it will also help you see if your thermometer is out as i did.

I went from doing brews that should have reached 5.5% alc.vol and were only fermenting out to 3.5-4%

Repalced the thermometer and my robust porter i estimated for 6.0% and is at 6.5% now and still fermenting!

(my efficiency increased by 4% aswell for some unknown reason.)

I would then like to know why Beersmith gives an estimated OG & FG dependent on only effieciency & volume , it doesn't take mashing style into account at all I've tried various mashes & no change ???

Any ideas.

Lagers

 

[Adamt]

Beersmith just estimates FG based on ingredients and yeast only.

 

[lagers44]

Thanks Adamt

The things you find out AFTER buying stuff ! <_<

 

[blackbock]

Final gravity is more closely connected with the amount/type of fermentables and also yeast strain, health and quantity than it does with mash temperature (although this may come into play where there is a simple grain bill, such as 100% Pilsner Malt.)

If I were you, I would set an arbitrary point to begin the diacetyl rest, such as S.G 1.022, or 4 days into fermentation or whatever you are confident you can reliably repeat instead of trying to guess what number the beer might drop down to.

Personally I've never felt the need for the rest.

 

[Fourstar]

If I were you, I would set an arbitrary point to begin the diacetyl rest, such as S.G 1.022, or 4 days into fermentation or whatever you are confident you can reliably repeat instead of trying to guess what number the beer might drop down to.

Personally I've never felt the need for the rest.

4 days, a S.G reading, high tide.

All of these are variables, use something thats a constant. In other words, when fermantion is steady for 2 days, rack it. OR use your palate and tase for diacetyl.

 

[blackbock]

4 days, a S.G reading, high tide.

All of these are variables, use something thats a constant. In other words, when fermantion is steady for 2 days, rack it. OR use your palate and tase for diacetyl.

When fermentation is steady for two days, FG has more or less been reached and this will not be helpful to predict final gravity in advance!

Using your palate to detect diacetyl before you have allowed yeast to reabsorb it also seems pretty pointless if you are planning to perform one of these rests.

 

[Fourstar]

When fermentation is steady for two days, FG has more or less been reached and this will not be helpful to predict final gravity in advance!

Using your palate to detect diacetyl before you have allowed yeast to reabsorb it also seems pretty pointless if you are planning to perform one of these rests.

Unless i have missed the point of the question, my reasoning was not to predict but to check for stable FG to begin you rest. What would be the reason why you would need to 'predict' todo a rest? Just await inactivity, ignore it for 2 days and you're done as long as you're yeast has fully attenuated. Ther'es nothing complex about it.

 

[Sprungmonkey]

I only wanted to know how to predict the FG as there are a few articles which say do a diacetyl rest 2/3 and one I read that said 1/2 way though fermentation. Is this right? What do you guys do. Should I just do the rest once fermentation is pretty much finished?

 

[razz]

If you can cool your wort to below pitching temp and then pitch yeast, you won't need to muck around with the D rest. That's IF.

 

[Fourstar]

I only wanted to know how to predict the FG as there are a few articles which say do a diacetyl rest 2/3 and one I read that said 1/2 way though fermentation. Is this right? What do you guys do. Should I just do the rest once fermentation is pretty much finished?

Not that i have done a lager and the chances of having diacetyl in my beer are relativly low, diacetyl is produced by fermentation and absorbed back by the yeast after fermentation. if you were todo a rest between fermentaiton you would risk getting a stuck ferment or risk a higher chance of diacetyl being present in your beer by stopping and starting. Essentially within 2 days after a stable FG, the yeast would have reabsorbed that diacetyl once present in your beer. rack from your primary vessel if you're concerned and crash chill to lager.

google 'diacetyl rest' and read the 1st link. Simple.

Cheers and enjoy the anti-pocorn beer!

 

[blackbock]

There are also hundreds of posts here on AHB and elsewhere about diacetyl rests. As far as I recall noone has ever reported a stuck ferment after raising the temperature of fermentation.

What you seem to be advocating is nothing more than, well, leaving the beer on the cake at the same temperature until FG is reached. ie. Not doing anything at all!

Raising the temperature a little before the final gravity is reached will increase the yeast's activity and the chances of them cleaning up any diacetyl. If the beer is infected, it is doomed anyway, and bacterial activity will also speed up the degradation of the beer.

Another thing you can do to minimise diacetyl is reduce the amount of aeration before pitching. But this can cause its own problems.

 

[Sprungmonkey]

Not that i have done a lager and the chances of having diacetyl in my beer are relativly low, diacetyl is produced by fermentation and absorbed back by the yeast after fermentation. if you were todo a rest between fermentaiton you would risk getting a stuck ferment or risk a higher chance of diacetyl being present in your beer by stopping and starting. Essentially within 2 days after a stable FG, the yeast would have reabsorbed that diacetyl once present in your beer. rack from your primary vessel if you're concerned and crash chill to lager.

google 'diacetyl rest' and read the 1st link. Simple.

Cheers and enjoy the anti-pocorn beer!

No worries - I google'd diacetyl rest and read the first link which actually said:

"If you're brewing a lager, try this trick: start allowing the fermentation temperature to rise once the beer has fermented to half its original gravity"

This is where I got a bit confused and was trying to predict the final gravity.

The beers i am brewing

Draught OG 1045 - after 8 days 1023 using Whitelabs San Fran Lager 65-70% Attenuation
Mexican Lager OG 1040 - after 8 days 1022 using White Labs Mexican Lager yeast 65-70% Attenuation
I measured the SG at day 6 and they both have only moved 3 points
both pitched at 20C and brewed at 11C (as it says on the white lab tubes).

Any thoughts comments etc?